Aromas are an important part of may products since consumers associate certain aromas with certain products. If the product lacks the aroma associated with it, consumer perception of the product is adversely affected. This is particularly a problem in the field of instant coffees, although it also exists in other fields. Instant coffee powders which are obtained from commercial processes involving extraction, concentration and drying, are usually substantially aroma-less. For this reason, it is conventional to recover coffee aromas which are given off during the processing of the instant coffee and to reincorporate these aromas into the concentrated coffee extract prior to drying or into the instant coffee powder.
The coffee aromas are recovered at several points during processing of the instant coffee and most commonly during grinding of the roasted beans and by steam stripping of the coffee extract prior to concentration and drying of the coffee solids.
The recovery of aroma from ground coffee is disclosed in U.S. Pat. No. 3,535,118. This patent discloses a process in which roast and ground coffee is placed in a column and maintained at about 40.degree. C. The bed of coffee is then moistened by spraying water on it to assist in displacing aromas from the coffee particles. An inert gas, usually nitrogen, is heated to about 44.degree. C. and introduced into the column from beneath the bed. As the inert gas passes up through the bed, it strips the aromas from the coffee particles. The inert gas is then fed to a condenser which is operated at a temperature of about 5.degree. C. to condense water in the inert gas. The de-watered inert gas is ultimately fed to a cryogenic condenser to condense the aroma as a frost. The frost is then recovered.
Another process for recovering aroma from roast and ground coffee is described in international patent application WO 97/10721. In this process, the ground coffee is transported through an elongated mixing zone while being agitated. At the same time, an aqueous fluid is sprayed into the elongated mixing zone to moisten the ground coffee as the ground coffee is being transported and agitated. A aroma gases released by the moistened ground coffee in the elongated mixing zone are drawn off and are collected. A similar processes are described in UK patent 1,466,881 and U.S. Pat. No. 4,092,436.
One of the problems perceived to arise with these processes is that they results in pre-wetting of the coffee grounds outside of the extraction cell or column. According to Sivetz, M and Desrosier N. W.; 1979; Coffee Technology. AVI Publishing Company, Inc., page 334, this practice is bad because it "causes staling of ground coffee in less than an hour, accompanied by a heavy, undesirable flavor and a loss in natural coffee volatiles". Sivetz and Desrosier strongly advocate that first wetting of the coffee grounds should occur in the extraction cell or column. Consequently recovery of aroma from ground coffee by pre-wetting it is not common practice; despite ground coffee being a good source of aroma.
Further, not all components of the aroma obtained in a cup of freshly brewed coffee are captured during pre-wetting. Consequently, unless further aroma is captured later during the process, some aroma components are lost; components which would, if incorporated into instant coffee powder, improve the aroma of a beverage prepared from the instant coffee powder. Further, many of the conventional recovery techniques damage or alter the aroma components.
Therefore there is still a need for a process for recovering aroma from ground coffee.